Broken Multi-D array

package  {
    import flash.display.Sprite;

    public class TileHolder extends Sprite{

        var gridSize:int = 50;

        var tiles:Array = [];

        public function TileHolder() {
            // constructor code
            generateTileGrid();
            trace(tiles.length)
            //trace(tiles[1][1])
            trace(getTileData(1,1))

        }

        function generateTileGrid(){
        for(var i:int = gridSize;i>0;i--){
        tiles.push(generateTileLine)
        }
        }

        function generateTileLine(){
        var a:Array = new Array();
        for(var i:int = gridSize;i>0;i--){
        a.push("1")
        }
        return a
        }

        function getTileData(X,Y){
        var tileData = tiles[Y][X]
        return tileData
        }


    }

}